The invention relates to a countercurrent sniffing leak detector including a mass spectrometer as a test gas detector, a high-vacuum pump or high-vacuum pump stage through which a test gas flows in countercurrent, a sniffing hose connected to the outlet side of the high-vacuum pump, or high-vacuum pump stage, respectively and a choke maintaining the pressure difference between atmospheric pressure in the inlet region of the sniffing hose and the pressure in the outlet region of the sniffing hose.
In order to attain in a leak detector of this type a short response time as well as high detection sensitivity, it is suggested that the sniffing hose is implemented such that the desired choking is achieved.
Through this measure it is achieved that the maximum allowed gas stream always passes through the sniffing hose. Since the leaks which are of interest in the helium test gas leak detection are on the order of magnitude of 10.sup.2 mbars/l/sec, it is ensured that the entire test gas stream escaping from a potentially present leak, is suctioned in and is transported into the leak detector. This results in a high detection sensitivity. Since, moreover, the flow rate in the sniffing hose, dimensioned according to the invention, is relatively high, a short response time also results. The cited advantages are attained especially well if the sniffing hose has a uniform diameter over its entire length so that it effects overall the desired choking. However, to solve the posed task it is already sufficient if only a relatively large segment of the sniffing hose, for example 50 or 75% of its length, has a choking function while the remaining segment conducts the gas to be investigated to the leak detector without significant resistance.
Sniffing leak detectors are known per se from DE-B-24 41 124. In this version of prior art described in this document, in the inlet region of the sniffing hose a choke is provided. The sniffing leak detector according to Patent Claim 1 of the cited document comprises a choke which is disposed directly in front of the mass spectrometer detector. In both versions it is unavoidable that a portion of the test gas streaming from a potentially present leak is carried into the inlet of the leak detector.